It has become increasingly important to treat wastewater in an efficient manner so as to protect the health and well being of humankind. In past years the treatment of wastewater has advanced considerably to include the use of biological as well as chemical agents. One example of these advancements is the now common practice of treating wastewater with biologically active organisms that digest, and thus eliminate, organic material from the wastewater. These biologically active organisms ("biomass") grow as a biofilm on support media that serve as carriers for the biologically active organisms. These biofilms, sometimes referred to as attached growth systems, are commonly grown on fixed surfaces that support the biomass. In many instances, the fixed surface area is quite large so as to accommodate the growth of a large amount of biomass for optimum efficiency of wastewater treatment.
In these attached growth systems, microorganisms growing on the fixed support media remove soluble contaminants from the wastewater by utilizing them as a source of energy for growth and production of new microorganisms. As new organisms form, the biological growth slowly becomes thicker, thereby resulting in anoxic conditions near the surface of the support media. As the bacterial mass builds, adhesion is weakened in the anoxic areas, and, as a result, the upper layers of the growth periodically "slough off." This sloughing off exposes a clean surface on which aerobic growth continues to accumulate.
The accumulation of biomass on the surfaces of the fixed support media also provides for entrapment of organic solids, which then are attacked by extracellular enzymes that solubilize the solids to make them available to the microorganisms as a further food source.
These processes take place in treatment plants that usually are buried underground. To access these plants, only small access openings in risers at grade level are provided. These grade level access openings allow an operator to perform routine inspection and maintenance of the aerator and biofilm support media. It is important to keep the grade level access openings small to improve aesthetics. Typically, the top of the underground tank is within 12 inches below the ground surface; however, this distance may be considerably greater than 12 inches for some installations, e.g., exceeding 60 inches or more. Thus, the risers connect to the underground wastewater treatment plants, and also provide access to the tanks from the ground level.
As a biomass grows, it begins to hinder the passage of wastewater through the biofilm support media. Therefore, the need to clean the support media in an efficient manner becomes critical. Unfortunately, the cleaning of support media has not enjoyed the same advancements as the treatment of wastewater. Thus, there is a need for an economical and efficient means by which an operator of a treatment facility can efficiently and easily clean and maintain the fixed support media in the treatment compartment or tank. Because the blocks of fixed support media can be quite large, it is highly desirable to clean the support media in the wastewater treatment tank, rather than removing the support media for cleaning outside the tank. Experience has shown that periodic cleaning of fixed support media enhances the overall performance and efficiency of a wastewater treatment system.
Currently used fixed support media cleaning apparatuses have several shortcomings that are difficult to overcome, and in many instances are a hindrance when cleaning and maintaining a wastewater treatment plant. These shortcomings include difficulty in cleaning the media in plants that utilize several risers, and that are accessible only through small ground level openings. To clean the BAT support media in the usual case, an operator must first remove the BAT support media from the underground wastewater treatment tank. The total cleaning process translates into great expenditures of time, resources, and money because the underground wastewater treatment tank first must be disassembled, followed by removing the support media, cleaning them, and placing them back into the wastewater treatment tank to await future tank reassembly.
Several inventors have disclosed the use of various devices for cleaning different types of tanks. For instance, U.S. Pat. No. 4,716,917 to Schmidt discloses a tank washing system, preferably for washing ship's tanks, that comprises several vertical rods having rotating nozzles attached by nozzle holders. The nozzles rotate via a complex gear system comprising a pivot bearing. The nozzle holder rotates via a drive and a drive member.
U.S. Pat. No. 4,859,249 to Valentini discloses a process for cleaning an enclosed vessel, wherein a telescoped housing utilizes a multi-nozzle rotating head. Similarly, U. S. Pat. No. 3,460,988 to Kennedy. Jr., et al. discloses an apparatus for spray treating boundary surfaces of enclosures, such as tanks. Disclosed in this invention is a sonic spray comprising a turret adapted to be driven about a vertical axis. The turret carries two sonic spray units on its opposing sides.
Another device for cleaning tanks is disclosed in U.S. Pat. No. 3,874,594 to Hatley. This device consists of a hollow shaft having a rotating nozzle attached at its distal end. The rotation of the nozzle is controlled by a worm gear mechanism located within the hollow shaft. The worm gear mechanism is driven by a complex gear system comprising a clutch and bevel gear mechanism placed within a housing attached to the upper end of the hollow shaft.
Another rotating nozzle device is described in U.S. Pat. No. 3,893,630 to Bochmann, et al. This device discloses a swivel outlet attached to a sprayer. The swivel outlet includes a first and second housing. The first housing includes a recessed cylindrical portion defined by cylindrical surfaces. A passageway extends radially outward from the recess of an enlarged portion designed to snugly receive the end of a discharge tube. The second housing includes a raised cylindrical housing dimensioned to fit snugly into the upper part of the recess of the first housing. A groove is provided about the cylindrical portion for seating an O-ring that functions to seal the cylindrical portion, while permitting rotation of the second housing with respect to the first housing about a common axis of the two cylindrical portions.
Other cleaning systems include those disclosed in U.S. Pat. Nos. 4,031,910 to Lawson, 4,805,650 to Yasui. et al., 5,460,193 to Levallois. et al., and 3,599,871 and Re. 27,612 to Ruppel, et al. The Lawson patent discloses an articulated spray applicator for cleaning flues comprising connected angular conduits having a plurality of orifices.
The Yasui, et al. patent discloses an apparatus for cleaning tanks comprising a support arm with a folding arm rotatably mounted to the lower end thereof.
The Levallois, et al. patent describes a device for cleaning the walls of a tank comprising a rotating stand equipped with at least one pressurized cleaning fluid spray element. The two Ruppel, et al. patents disclose a jet spray cleaner comprising a collapsible mechanism with a plurality of rotating jet nozzles that are driven by gears.
In order to effectively service BAT media located within a wastewater treatment tank, a new apparatus and method of cleaning BAT media is needed which will allow easy periodic cleaning and maintenance of fixed biofilm support media without the need to first remove the biofilm from the wastewater treatment plant. In addition, a new apparatus and method of cleaning BAT support media is needed that also will accommodate a range of sizes and configurations of ground level openings, including various risers.